This invention relates to the use of 3- and/or 4-substituted pyrrolidines as catalysts for the manufacture of products by the polyisocyanate polyaddition process. These catalysts may be used as substitutes or in combination with known urethane catalysts, such as 1,4-diazobicyclo[2.2.2]octane (DABCO) for the production of rigid or flexible polyurethane foams and numerous other polyurethane products. The term "polyurethane products" as used herein is to be understood to include all products of reaction of polyisocyanates with compounds having at least two isocyanate-reactive hydrogen atoms; that is, the term polyurethane is used to denote, for example, pure polyurethanes, polyurethane polyureas, and pure polyureas.
The rate of the reaction between isocyanate groups and compounds containing isocyanate-reactive hydrogen atoms is influenced not only by the temperature of the starting products and their structure but particularly also by the use of suitable catalysts. In practice, bases (for example, tertiary amines such as triethylamine) are used mainly as nucleophilic catalysts, whereas organometallic compounds (for example, tin carboxylates such as tin(II) octoate) are used mainly as electrophilic catalysts. The use of Lewis acids together with Lewis bases, which is normally characterized by synergistic effects, is state of the art. It is also known, however, that amines are used as the only catalyst for numerous purposes. Among the large number of known amine Catalysts (see Ullmann 4th Edition and Kunststoffhandbuch Volume VII, Polyurethane, Hansen-Verlag, Munich (1983)), only relatively few have hitherto been widely used industrially, with 1,4-diazabicyclo[2,2,2]octane, bis(2-dimethylaminoethyl) ether, triethylamine, dimethylcyclohexylamine, dimethylethanolamine, dimethylbenzylamine, methylmorpholine, and ethylmorpholine, being the most important. One would, of course, mainly use those catalysts which are distinguished by high activity, economical method of preparation, and breadth of application.
Another increasingly important consideration is the toxicological evaluation of the catalysts with regard to their safety in use and freedom from odor. Many of the amine catalysts used today, such as DABCO or triethylamine, may be regarded as unsatisfactory in this respect because of their high volatility and relatively intense amine odor that persists in the end product produced with the aid of such catalysts. In view of the many possible applications of polyurethane resins, it is equally desirable to provide "tailor-made" catalysts adapted to the individual requirements. One possibility lies in chemically modifying a type of catalyst to adjust its activity to its particular purpose.
It has now surprisingly been found that certain pyrrolidine derivatives can advantageously be used as catalysts for the preparation of polyurethanes. Compared with the above-mentioned amine catalysts, the compounds according to the invention have a comparable or even higher activity. Another welcome effect of the catalysts according to the invention is that the activity of the products can be adjusted exactly as required by suitable choice of the substituents on the ring, in contrast to, for example, DABCO, which allows no variation within economically acceptable limits. Another advantage of the catalysts of the invention is the very faint odor and low volatility of the compounds, which are in part bound in the polymer by isocyanate-reactive groups so that the odor is considerably reduced in the preparation of polyurethane products. Other advantages may also be observed, including, for example, the ease of handling (because the pyrrolidines that are preferably used are liquid), the advantageous rate of hardening, and, not least, the very simple method by which some of these compounds may be prepared.